1. Field of the Invention
The present invention relates to an optical pickup for exposing a laser beam passed through a diffraction grating to an optical disk, a tilt detection apparatus, a tilt detection method for detecting a tilt of the optical disk, and an optical disk apparatus.
2. Description of the Related Art
In the optical disk apparatus, when a tilt exists on the optical disk, the deterioration of the signal quality of a recording signal and/or a reproducing signal of the optical disk may be occurred. For correcting the tilt of the optical disk, it is necessary to detect the tilt of the optical disk and generate a signal in response to the tilt.
An invention of an optical pickup is disclosed in Japanese Unexamined Patent Publication (Kokai) No.9-128785. In this Publication, in an optical pickup comprising a laser beam source, an objective lens and an aberration correction use liquid crystal panel, it is disclosed to change the refractive index of the liquid crystal panel in response to the thickness or the tilting angle of the liquid crystal panel.
Further, it is disclosed that a tilt sensor detects the tilting angle and a liquid crystal panel control circuit drives the liquid crystal panel to change the refractive index based on the tilting angle.
In the optical pickup of said Publication No.9-128785, the position for arranging the tilt sensor is restricted, and, in the optical disk, a point to which the laser beam is exposed is different from a point where the tilt sensor detects the tilt, and thus it is difficult to detect the tilt of the optical disk precisely.
An object of the present invention is to provide a tilt detection apparatus and a tilt detection method capable of detecting a tilt of an optical disk.
Further, another object of the present invention is to provide an optical pickup applicable in said tilt detection apparatus.
Further, still another object of the present invention is to provide an optical disk apparatus.
A first optical pickup according to the present invention comprises a laser for outputting a laser beam; a diffraction grating for diffracting the laser beam from said laser to generate a 0th order diffraction beam and +-first order diffraction beams; an objective lens for collecting said 0th order diffraction beam and said +-first order diffraction beams and exposing the beams to an optical disk on which track guide grooves are formed; and a photodetector for generating signals in response to said +-first order diffraction beams reflected at said optical disk, and each of said +-first order diffraction beams exposed to said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted, and said photodetector comprises light receiving portions for receiving each of said +-first order diffraction beams reflected at said optical disk, and each of said light receiving portions is divided in the direction in response to the track direction on said optical disk.
In the first optical pickup according to the present invention, preferably, said objective lens collects said 0th order diffraction beam and exposes it to the track of said optical disk, and a distance from the center part of the optical spot of said 0th order diffraction beam to the center part of the optical spots of said +-first order diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the first optical pickup according to the present invention, preferably, said phase distribution of one of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
In the first optical pickup according to the present invention, preferably, it further comprises an actuator for moving said objective lens in the disk radial direction in response to an eccentricity of said optical disk, and a position sensor for detecting the quantity of movement or the quantity of change of said objective lens.
A second optical pickup according to the present invention comprises a laser for outputting a laser beam, a first diffraction grating for diffracting the laser beam from said laser to generate a main laser beam including a 0th order diffraction beam and first and second sub laser beams including one of +-first order diffraction beams, a second diffraction grating for diffracting said main laser beam to generate a main laser diffraction beam including a 0th order diffraction beam and third and forth sub laser diffraction beams including one of +-first order diffraction beams and diffracting said first and second sub laser beams to generate first and second sub laser diffraction beams including a 0th order diffraction beam, an objective lens for collecting said main laser diffraction beams and said first to forth sub laser diffraction beams and exposing the beams to an optical disk on which track guide grooves are formed, and a photodetector for generating signals in response to said main laser diffraction beams and said first to forth sub laser diffraction beams reflected at said optical disk, and each of said first and second sub laser diffraction beams exposed to said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted.
In the second optical pickup according to the present invention, preferably, said objective lens collects said main laser diffraction beam and exposes it to the track of said optical disk, and a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said first and second sub laser diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the second optical pickup according to the present invention, preferably, a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said third and forth sub laser diffraction beams in the disk radial direction is, when m is an integer of 0 or more, equal to or approximately equal to a (m+xc2xd) times of the pitch of said track or said track guide groove.
In the second optical pickup according to the present invention, preferably, said phase distribution of one of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
In the second optical pickup according to the present invention, preferably, said photodetector comprises light receiving portions for receiving each of said main laser diffraction beam and said first to forth sub laser diffraction beams reflected at said optical disk, and each of said light receiving portions is divided in the direction in response to the track direction on said optical disk.
In the second optical pickup according to the present invention, for example, it may be made the configuration which said wave front aberration is the coma aberration generated at a transparency substrate of said optical disk.
A first tilt detection apparatus according to the present invention comprises a laser for outputting a laser beam, a diffraction grating for diffract the laser beam from said laser to generate a 0th order diffraction beam and +-first order diffraction beams, an objective lens for collecting said 0th order diffraction beam and +-first order diffraction beams and exposing the beams to the optical disk on which track guide grooves are formed, a generating circuit for generating push-pull signals of said +-first order diffraction beams reflected at said optical disk, and a detection circuit for detecting a tilt of said optical disk based on the sum of the push-pull signals of said +-first order diffraction beams, and each of said +-first order diffraction beams exposed to said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted.
In the first tilt detection apparatus according to the present invention, preferably, said objective lens collects said 0th order diffraction beam and exposes it to the track of said optical disk, and a distance from the center part of the optical spot of said 0th order diffraction beam to the center part of the optical spots of said +-first order diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the first tilt detection apparatus according to the present invention, preferably, said phase distribution of one of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
In the first tilt detection apparatus according to the present invention, preferably, it further comprises a photodetector, said photodetector comprises light receiving portions for receiving each of said +-first order diffraction beams reflected at said optical disk, and each of said light receiving portions is divided in the direction in response to the track direction on said optical disk, and said generating circuit generates the push-pull signals of said +-first order diffraction beams based on the output signals from said light receiving portions of said photodetector.
In the first tilt detection apparatus according to the present invention, preferably, it further comprises an actuator for moving said objective lens in the disk radial direction in response to an eccentricity of said optical disk, and a position sensor for detecting the quantity of movement or the quantity of change of said objective lens, and said detection circuit generates an eccentricity signal in response to the eccentricity of said optical disk based on said quantity of movement or the quantity of change detected by said position sensor and detecting a tilt of said optical disk based on the deference between the sum of the push-pull signals of said +-first order diffraction beams and said eccentricity signal.
A second tilt detection apparatus according to the present invention comprises a laser for outputting a laser beam, a first diffraction grating for diffracting the laser beam from said laser to generate a main laser beam including a 0th order diffraction beam and first and second sub laser beams including one of +-first order diffraction beams, a second diffraction grating for diffracting said main laser beam to generate a main laser diffraction beam including a 0th order diffraction beam and third and forth sub laser diffraction beams including one of +-first order diffraction beams and diffracting said first and second sub laser beams to generate first and second sub laser diffraction beams including a 0th order diffraction beam, an objective lens for collecting said main laser diffraction beam and said first to forth sub laser diffraction beams and exposing the beams to an optical disk on which track guide grooves are formed, a generating circuit for generating push-pull signals of said main laser diffraction beam and said first to forth sub laser diffraction beams reflected at said optical disk, and a detection circuit for generating an eccentricity signal in response to the eccentricity of said optical disk based on the push-pull signals of said main laser diffraction beam and said third and forth sub laser diffraction beams and detecting a tilt of said optical disk based on the deference between the sum of the push-pull signals of said first and second sub laser diffraction beams and said eccentricity signal, and each of said first and second sub laser diffraction beams exposed to said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted.
In the second tilt detection apparatus according to the present invention, preferably, said objective lens collects said main laser diffraction beam and exposes it to the track of said optical disk, and a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said first and second sub laser diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the second tilt detection apparatus according to the present invention, further preferably, a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said third and forth sub laser diffraction beams in the disk radial direction is, when m is an integer of o or more, equal to or approximately equal to a (m+xc2xd) times of the pitch of said track or said track guide groove.
In the second tilt detection apparatus according to the present invention, preferably, said phase distribution of one of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
In the second tilt detection apparatus according to the present invention, preferably, it further comprises a photodetector, and said photodetector comprises light receiving portions for receiving each of said main laser diffraction beams and said first to forth sub laser diffraction beams reflected at said optical disk, and each of said light receiving portions is divided in the direction in response to the track direction on said optical disk, and said generating circuit generates the push-pull signals of said main laser diffraction beam and said first to forth sub laser diffraction beams based on the output signals from said light receiving portions of said photodetector.
A first tilt detection method according to the present invention comprises the steps of diffracting a laser beam to generate a 0th order diffraction beam and +-first order diffraction beams and exposing said generated 0th order diffraction beam and +-first order diffraction beams to an optical disk on which the track guide grooves are formed, generating push-pull signals of said +-first order diffraction beams reflected at said optical disk, and detecting the tilt of said optical disk based on the sum of the push-pull signals of said +-first order diffraction beams, and each of said +-first order diffraction beams reflected at said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted.
In the first tilt detection method according to the present invention, preferably, said exposing step has the steps of collecting said 0th order diffraction beam and +-first order diffraction beams and exposing said 0th order diffraction beam to the track of said optical disk, and a distance from the center part of the optical spot of said 0th order diffraction beam to the center part of the optical spots of said +-first order diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the first tilt detection method according to the present invention, preferably, said phase distribution of one of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said +-first order diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
In the first tilt detection method according to the present invention, preferably, ut further comprises the step of generating an eccentricity signal in response to the eccentricity of said optical disk, and said detecting step has a step of detecting the tilt of said optical disk based on the difference between the sum of the push-pull signals of said +-first order diffraction beams and said eccentricity signal.
A second tilt detection method according to the present invention comprises the steps of diffracting the laser beam to generate a main laser beam including a 0th order diffraction beam and first and second sub laser beams including one of +-first order diffraction beams, diffracting said main laser beam to generate a main laser diffraction beam including a 0th order diffraction beam and third and forth sub laser diffraction beams including one of +-first order diffraction beams and diffracting said first and second sub laser beams to generate first and second sub laser diffraction beams including a 0th order diffraction beam, exposing said main laser diffraction beam and said first to forth sub laser diffraction beams to an optical disk on which track guide grooves are formed, generating push-pull signals of said main laser diffraction beam and said first to forth sub laser diffraction beams reflected at said optical disk, and generating an eccentricity signal in response to the eccentricity of said optical disk based on the push-pull signals of said main laser diffraction beam and said third and forth sub laser diffraction beams and detecting a tilt of said optical disk based on the deference between the sum of the push-pull signals of said first and second sub laser diffraction beams and said center eccentricity signal, and each of said first and second sub laser diffraction beams exposed to said optical disk has the phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on said optical disk when said optical disk is tilted.
In the second tilt detection method according to the present invention, preferably, said exposing step has a step of collecting said main laser diffraction beam and said first to forth sub laser diffraction beams and exposing said main laser diffraction beam to the track of said optical disk, and a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said first and second sub laser diffraction beams in the disk radial direction is, where n is an integer of 0 or more, equal to or approximately equal to a (n/2+xc2xc) times of the pitch of said track or said track guide groove.
In the second tilt detection method according to the present invention, further preferably, a distance from the center part of the optical spot of said main laser diffraction beam to the center part of the optical spots of said third and forth sub laser diffraction beams in the disk radial direction is, when m is an integer of 0 or more, equal to or approximately equal to a (m+xc2xd) times of the pitch of said track or said track guide groove.
In the second tilt detection method according to the present invention, preferably, said phase distribution of one of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a positive constant angle, and said phase distribution of another of said first or second sub laser diffraction beams is a phase distribution generated when the tilting angle of said optical disk is a negative constant angle.
An optical disk apparatus according to the present invention comprises an optical pickup for diffracting a laser beam from a laser, generating a 0 order diffraction beam and +-first order diffraction beams having the phase distribution equal to or approximately equal to the phase distribution due to the wave front aberration of an optical disk when the optical disk is tilted, exposing the 0 order diffraction beam and +-first order diffraction beams to the optical disk, and receiving reflected beams of said exposed beams from the optical disk to generate signals in response to each of the reflected signals, a signal generation circuit for generating push-pull signals of said received reflected beams of at least said +-first order diffraction beams, a tilt detection circuit for detecting the tilt of the optical disk based on the sum of said generated push-pull signals of said +-first order diffraction beams, and a tilt correction portion for correcting the tilt of the optical disk in response to said detected tilt.
In the first tilt detection apparatus according to the present invention mentioned above, the +xe2x88x92primary diffraction beams generated by the diffraction grating have a phase distribution equal to or nearly equal to the phase distribution due to the wave front aberration generated on the optical disk while the optical disk has a tilt.
By said phase distribution, the push-pull signal of one of the +xe2x88x92primary diffraction beams becomes the maximum value at the certain tilt angle (xcex8) and the push-pull signal of another of the +xe2x88x92primary diffraction beams becomes the minimum value at the certain tilt angle (xe2x88x92xcex8). By obtaining an additional signal as the result of addition of the push-pull signals of the +xe2x88x92primary diffraction beams, the value of the additional signal can be made 0 while the tilt angle of the optical disk is 0xc2x0 and the symmetrical additional signal corresponding to the positive and negative tilt angles can be obtained, so that the tilt angle is detectable by the additional signal.
In the second tilt detection apparatus according to the present invention mentioned above, the first and second sub laser diffraction beams generated by the first and second diffraction gratings have a phase distribution equal to or substantially equal to the phase distribution due to the wave front aberration generated on the optical disk while the optical disk has a tilt.
By said phase distribution, the push-pull signal of one of the first and second sub laser diffraction beams becomes the maximum value at the certain tilt angle (xcex8) and the push-pull signal of another of the first and second sub laser diffraction beams becomes the minimum value at the certain tilt angle (xe2x88x92xcex8). By obtaining an additional signal as the result of addition of the push-pull signals of the first and second additional beams, the value of the additional signal can be made 0 while the tilt angle of the optical disk is 0xc2x0 and the symmetrical additional signal corresponding to the positive and negative tilt angles can be obtained, so that the tilt angle is detectable by the additional signal.